1. Field of the Invention
The present invention relates generally to the field of centrifuge systems. More particularly, the present invention relates to detecting and controlling imbalance conditions in a centrifuge system.
2. Discussion of the Related Art
Rotors for centrifuge systems are typically well balanced and run smoothly across the speed range through which they are rotated. The addition of samples to the rotor creates the potential situation for the rotor to be out of balance. This causes unwanted motion in the motor and the mounting system as the mechanical system (including the motor, rotor, and mounting system) rotates about the new center of gravity determined by the size and position of the imbalance. The response of this mechanical system will exhibit resonant peaks due to the flexibility and mass of the motor, the mounting system, and the cabinet. Thus, as the motor is brought up to speed, the vibrations caused by the imbalance will result in a displacement of the motor and the mounting system. As the motor is brought up to speed, the resonant peaks will induce peaks in the amplitude of the motor motion. The amplitudes of these displacements are limited by the fact that the physical structure of the machine gets in the way and the motor/rotor/mounting system may come into contact with the structure of the machine. In particular, the rotor should not be allowed to hit other parts of the centrifuge system in order to avoid damage or destruction.
Further consequences of operating the centrifuge system when there is an imbalance in the motor/rotor/mounting system may be increased noise, possible sample resuspension (especially at acceleration/deceleration as the speed moves through the resonant peaks), and excessive vibration and machine movement.
Two conventional approaches to measuring the motion of the motor/rotor/mount system due to the out of balance condition are:
1. A mechanical arm is positioned such that when the motion becomes large enough, the arm trips a switch, and this switch closure is detected by the control system and appropriate action is taken, such as shutting the system down.
2. A magnetic switch, consisting of a small permanent magnet and Hall effect sensor is used to perform the same function as the mechanical arm. In this case, the magnet is positioned above the sensor, linked to the motor/rotor/mount system. When the motor position moves sufficiently to bring the magnet closer to the Hall effect sensor, the increased magnetic field trips the sensor and this is detected by the control system to take appropriate action, such as shutting the system down.
Both of these systems are typically manually adjusted during manufacture to work reliably, i.e. within the range of imbalance that has been determined to match the particular machine design.
The present invention provides an apparatus for controlling a centrifuge system, the centrifuge system including a rotor and a motor operatively coupled to the rotor, the apparatus comprising an accelerometer coupled to the centrifuge system so as to measure an acceleration of at least a portion of the centrifuge system during operation of the centrifuge system to provide an acceleration signal, and a controller that receives the acceleration signal and controls the centrifuge in response to the acceleration signal.
According to an embodiment of the invention, the controller compares the acceleration signal with a reference signal and provides a control signal when a magnitude of the acceleration signal is larger than the magnitude of the reference signal.
According to an embodiment of the invention, the centrifuge system is shut down in response to the control signal.
According to an embodiment of the invention, the rotational speed of the rotor is reduced in response to the control signal.
According to an embodiment of the invention, the acceleration signal is a voltage.
According to an embodiment of the invention, the acceleration signal is a current.
According to an embodiment of the invention, the acceleration is in a radial direction.
According to an embodiment of the invention, the acceleration is in a longitudinal direction.
According to an embodiment of the invention, the acceleration is in a direction generally perpendicular to an axis of rotation of the rotor.
According to an embodiment of the invention, the acceleration is in a direction generally perpendicular to an axis of rotation of the motor.
According to an embodiment of the invention, the acceleration is the result of an imbalance condition in the rotor.
According to an embodiment of the invention, the accelerometer is an integrated circuit.
According to an embodiment of the invention, the accelerometer is a monolithic integrated circuit.
According to an embodiment of the invention, the acceleration is caused by vibrations of the rotor having a range of frequencies when the rotor is spinning and wherein the apparatus further comprises means for determining a range of frequencies that the accelerometer will sense.
According to an embodiment of the invention, the apparatus further comprises a filter that receives the acceleration signal from the accelerometer and provides a filtered acceleration signal to the controller.
According to an embodiment of the invention, the filter comprises a high-pass filter.
According to an embodiment of the invention, the filter comprises a bandpass filter.
According to an embodiment of the invention, the filter comprises a low-pass filter.
According to an embodiment of the invention, the low-pass filter comprises an integrator that receives the acceleration signal and integrates the acceleration signal to provide a displacement signal that represents a displacement of at least one of the motor and the rotor of the centrifuge system and wherein the controller receives the displacement signal and controls the centrifuge system in response to the displacement signal.
According to an embodiment of the invention, the integrator integrates the acceleration signal to provide a velocity signal and then integrates the velocity signal to provide the displacement signal.
According to an embodiment of the invention, the integrator includes an operational amplifier and a capacitor.
According to an embodiment of the invention, the displacement signal is a voltage.
According to an embodiment of the invention, the displacement signal is a current.
According to an embodiment, the invention includes a method of controlling a centrifuge system, the centrifuge system including a rotor and a motor operatively coupled to the rotor, the method comprising the steps of measuring an acceleration of at least a portion of the centrifuge system during operation of the centrifuge system to provide an acceleration signal and controlling the centrifuge system in response to the displacement signal.
According to an embodiment of the invention, the step of controlling the centrifuge system further comprises comparing the acceleration signal with a reference signal and providing a control signal when a magnitude of the acceleration signal is larger than a magnitude of the reference signal.
According to an embodiment of the invention, the control signal shuts off the centrifuge system.
According to an embodiment of the invention, the centrifuge system responds to the control signal to reduce a rotational speed of the rotor.
According to an embodiment of the invention, the step of determining a range of frequencies includes filtering the range of frequencies to provide a filtered acceleration signal.
According to an embodiment of the invention, the step of filtering the range of frequencies includes high-pass filtering the range of frequencies.
According to an embodiment of the invention, the step of filtering the range of frequencies including band-pass filtering the range of frequencies.
According to an embodiment of the invention, the step of filtering the range of frequencies includes low-pass filtering the range of frequencies.
According to an embodiment of the invention, the step of low-pass filtering further comprises the step of integrating the acceleration signal to provide a displacement signal that represents a displacement of at least one of the motor and the rotor of the centrifuge system and wherein the step of controlling the centrifuge system includes controlling the centrifuge system in response to the displacement signal.
According to an embodiment of the invention, the step of integrating further includes integrating the acceleration signal to provide a velocity signal and then integrating the velocity signal to provide the displacement signal.
According to an embodiment of the invention, the acceleration is caused by vibrations of the rotor having a range of frequencies and wherein the method further comprises the step of determining a range of frequencies that will be sensed when measuring the acceleration.
The features and advantages of the present invention will be more readily understood and apparent from the following detailed description of the invention, which should be read in conjunction with the accompanying drawings, and from the claims which are appended at the end of the Detailed Description.